Oil which may be present in subterranean rock formations can generally be removed by drilling and allowing pressure within the oil field to force the oil up to the borehole. When the existing over pressure diminishes, an artificial oil pressure can be accomplished by injecting water into the formation to flush out additional free oil in a process known as secondary removal.
Oil present in tar sands can generally be removed by agitation, heat, and mixing in a process to remove the oil by floatation. Skimming can be used to remove additional oil in aqueous runoff from this process. It is known that tailings from these treated tar sands can still contain a high percentage of hydrocarbons.
For many types of soils, following secondary removal a great deal of oil remains. For certain geological materials, oil remaining after secondary removal may easily exceed 50% of the volume of removed oil. The remaining oil-bearing geological formation contains a substantial amount of oil within its pores or channels.
A portion of this residual oil can be displaced by microorganisms using microbial enhanced oil recovery (MEOR) in which the metabolism of the microorganisms causes displacement of the oil that may subsequently be recovered by the production wells.
In U.S. Pat. No. 4,522,261 which is incorporated herein by reference, it is disclosed to use surfactant producing Bacillus licheniformis which is useful for solubilizing oil. These surfactants may be used by direct injection into the reservoir in order to avoid plugging difficulties. However, it is also known that microbes can be injected into production wells to increase the yield of recovered oil.
U.S. Pat. No. 4,905,761, which is incorporated herein by reference, describes a microbial enhanced oil recovery process in which microorganisms are introduced by injection wells along with a nutrient solution for obtaining additional oil from oil-bearing reservoirs. The process includes using a first species of a microorganism to secrete a surfactant, a second species of microorganism that secretes a solvent which, in combination, provides for displacement of oil such that additional oil may be recovered from the well.
It is also known in the art to use various nutrients such as vitamins, phosphates, and various electron donors so as to stimulate native bacteria or to introduce bacteria so as to create a sufficient biomass layer which acts to disassociate the oil from the rock/soil formation thereby permitting the disassociated oil to be collected. One such process is described in U.S. Pat. No. 6,758,270 which is incorporated herein by reference.
The waste hydrocarbons from the existing processes are of major environmental concern. Tailings and oil bearing runoffs from these inefficient oil recovery processes can potentially contaminate nascent surface water, groundwater, sediments, and soil for years. In addition other chemicals, such as paraffins, are frequently added to the tars sands to enhance hydrocarbon removal. While aeration is used to remove some of these paraffins, residual paraffins remain and contaminate the water runoff. Paraffins are thus a growing regulatory concern.
It is also known in the art that hydrocarbon extraction can involve the mining of tar sands as part of an above-ground recovery process. The tar sands, even after conventional processing and treatment, contain a high percentage of hydrocarbons which are not readily extractable. The waste product from a tar sands recovery process still has a high percentage of hydrocarbons which cannot be readily separated using conventional technologies. Further, it is also known that hydrocarbon recovery from tar sands and similar processes will result in bitumen froth tailings which also have a high level of hydrocarbons that pose environmental hazards. There remains a need for an ability to both enhance recovery of viable product from such waste tailings as well as degrading any remaining unrecoverable hydrocarbon content so as to prevent environmental contamination from the tailings and hydrocarbon recovery waste.
While there is a great deal of teaching directed to use of microorganisms to enhance petroleum recovery, there remains room for improvement and variation within the art.